1. Field of the Invention
Digoxin, and derivatives of digoxin, find wide use in cardiac treatment, frequently as a component of digitalis. Digoxin is highly potent in its activity and has a narrow therapeutic range. In addition, the drug can produce serious side effects, so that monitoring the digoxin level in blood is important for the well-being of the patient.
Since the therapeutic range is from about 0.8 to 2.0 ng/ml, it is necessary no only to measure extremely small amounts of digoxin in serum, but also to be able to distinguish between small differences in concentrations. Depending upon the sensitivity of the assay, the digoxin concentration in serum may be insufficient for detection when diluted into the assay medium. Also, naturally occurring materials in the serum sample may modify the observed signal so as to give false results. It would therefore be desirable to provide for a simple means for pretreatment of a serum sample for a digoxin assay. The pretreatment method should be rapid and efficient and provide an assay sample containing the drug in a concentrated amount free of interfering substances.
2. Description of the Prior Art
A radioimmunoassay for determining the digoxin content of a sample is disclosed in U.S. Pat. No. 3,981,982. An enzyme amplification assay is described in U.S. Pat. No. 3,817,837.